This invention relates in general to a magnetic head assembly for use in magnetic media reproduction systems such as magnetic tape recorders. More particularly, this invention relates to a magnetic head assembly which includes a plurality of magnetic heads bonded into a single piece faceplate of magnetic ferrite which provides effective magnetic shielding between magnetic heads and a stable and long life mechanical structure.
Magnetic head assemblies used in magnetic tape recorders and magnetic disc drives must meet more demanding design specifications necessitated by high density recording formats. Thus, in a high density magnetic tape recorder, the tape bearing surfaces (such as magnetic head tips and non-magnetic faceplate surfaces) must be durable in order to provide long head life despite high pressure contact over the head gap area with highly abrasive magnetic tape media (such as chromium dioxide tape). The faceplate and heads should have compatible wear properties to prevent head undercut and separation loss. Moreover, the magnetic head assembly must have mechanical stability and be able to withstand environmental changes (temperature, humidity, shock and vibration) without performance degradation. The magnetic head core structure must be optimized to minimize crosstalk between heads in adjacent tracks and between read and write heads in the same track. The magnetic head assembly should also have a cost effective design in order to be competitive in a highly cost sensitive market.
Numerous proposals have been made to utilize both magnetic and non-magnetic ferrite materials in magnetic head assembly design. High density ferrites are generally mechanically stable;are highly resistant to abrasion; and provide good magnetic signal recording and reproduction characteristics. Typically, a multi-channel magnetic head assembly has been formed from a large number of individual elements. A typical head assembly, which is made of two half brackets (or two half shells) screwed and epoxied together, would include individual ferrite (or metal) cores wound with the necessary turns of electrical conductor. The cores are then (1) loaded into the half brackets, (2) cemented in place, and (3) connected to electrical terminal boards or electrical connector plates inserted into the bottom of the half brackets. Tip plates (which form the front surface of the magnetic head assembly) are slotted to accommodate intertrack magnetic shields and grooved to receive magnetic head tip pieces which are especially hard and durable. The tip plates are then attached to the loaded half brackets providing intimate contact between the tip pieces and the top of the ferrite cores. The magnetic gap of each head is then formed by vacuum deposition of silicon monoxide and the two half brackets bonded together. The front surface contacting the tape is then contoured (see for example, the Bell & Howell publication entitled, "MAGNETIC TAPE RECORDING TECHNICAL FUNDAMENTALS", 4th printing revised, 1984, pp. 23 et. seq.; "THE COMPLETE HANDBOOK OF MAGNETIC RECORDING", by Jorgensen, 1980 ed., pub. by TAB Books, Inc., Blue Ridge Summit, PA, pp. 158 et seq.; and U.S. Pat. No. 3,400,386, entitled "Multichannel Magnetic Read Assembly", issued Sept. 3, 1968, by R.C. Sinnott). Such magnetic head assemblies are disadvantageous because of the difficulty and expense in producing them. Moreover, the number of assemblies which must be discarded due to incorrect component positioning is high.
Multichannel magnetic head assemblies have also been proposed, in which a plurality of magnetic ferrite heads are bonded to a split non-magnetic ferrite faceplate. Individual magnetic shields are secured between adjacent heads to minimize crosstalk and the structure mounted in an aluminum shell (see for example, U.S. Pat. No. 3,668,775 issued June 13, 1972, entitled "Method for Manufacturing Magnetic Heads", by Morita et al; and U.S. Pat. No. 3,789,505, issued Feb. 5, 1974 entitled "Method Of Making a Multi-Core Magnetic Head With A Non-Magnetic Holder" by R.L. Huntt). Such magnetic head assemblies are disadvantageous in the use of individual magnetic shields between adjacent heads and in the use of different ferrite materials in the faceplate structure thus increasing mechanical instabilities.
Magnetic head assemblies are also known in which magnetic ferrite cores are mounted in non-magnetic ferrite holders and individual magnetic ferrite shields are inserted between adjacent magnetic heads (see for example, U.S. Pat. No. 3,909,932, issued Oct. 7, 1975, entitled "Method of Manufacturing A Multi-Track Magnetic Head", by W.L. Kroon; U.S. Pat. No. 3,842,494, issued Oct. 22, 1974 entitled "Multi-Channel Magnetic Ferrite Head And A Method For Making The Same", by H. Chiba et al; and U.S. Pat. No. 3,761,641 issued Sept. 25, 1973, entitled "Magnetic Head With Demountable Face Part Assembly", by T.A. Mlinarick). Each of the magnetic head assemblies disclosed in these patents is disadvantageous because of the large number of parts required to form the magnetic head assembly and because of the difficulty in properly aligning the magnetic head gaps across the width of the assembly. Such magnetic head assemblies are also complex and expensive to produce.
In order to reduce the number of individual parts used in a multi-head magnetic head assembly and in order to effect exact alignment of magnetic head gaps across the width of the head assembly, it has been proposed to form a plurality of individual heads from blocks of magnetic ferrite. The magnetic ferrite blocks are ground down to form individual magnetic head core pieces. The structure is lapped, gapped and bonded to form a multi-head magnetic assembly. The individual heads may be commonly joined together by a portion of the magnetic ferrite block which is not removed. Such assemblies are disclosed in U.S. Pat. No. 3,544,982, issued Dec. 1, 1970, entitled "Multi-Head Magnetic Assembly", by J.J. Hanak. As disclosed, the rear portion of the magnetic heads is commonly joined by a solid magnetic ferrite piece which is integral with the individual head cores. U.S. Pat. No. 3,543,396, issued Dec. 1, 1970 entitled "Method Of Multi-Track, Two-Gap, Ferrite Magnetic Heads Design Especially For Digital Recording", by Z. Illg et al, discloses a magnetic head assembly in which three blocks of magnetic ferrite are lapped, gapped and bonded together. The bonded structure is ground down to provide a multi-track magnetic head assembly in which each track has a pair of in line heads separated from each other. In the embodiments shown in FIGS. 6 and 7, a centrally disposed solid magnetic ferrite piece runs the width of the head assembly and is integral with the inner core leg of each head in the assembly. These magnetic head assemblies are disadvantageous (1) in using separate magnetic shields between adjacent heads and between in-line heads and (2) in using an integral magnetic ferrite shunt between adjacent heads in the magnetic assembly which increases the likelihood of crosstalk between heads in the same track and between heads in adjacent tracks.